1. Plasma levels of atrial natriuretic peptide (ANP) were measured by radioimmunoassay in eight normal healthy volunteers before and during mineralocorticoid escape.

2. Mean plasma ANP on a fixed sodium intake before fludrocortisone was 6.5± sem 1.1 pg/ml. Within 24 h of fludrocortisone administration there was a significant increase in plasma ANP which continued to increase daily reaching a plateau by day 4 (14.9 ± 2.4 pg/ml) to day 7 (15.1 ± 2.6 pg/ml).

3. The rise in plasma ANP was closely related to the amount of sodium retained during the fludrocortisone treatment and the sodium ‘escape’ occurred by days 4 to 7.

4. These results support the concept that ANP could play an important hormonal role in overcoming the sodium-retaining effects of mineralocorticoids in man.

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